The strategic use of estradiol to enhance fertility and submission rates of progestin-based estrus synchronization programs in dairy herds

Two experiments were performed to evaluate the efficacy of a progestin-base d estrus synchronization program that incorporated the use of estradiol at the initiation of progestin treatment and at 48 h after progestin withdrawa l (Exp. 2). In Exp. 1, cyclic, lactating dairy cows (n = 112) were assigned to receive either 1 (1mg) or 2 (2mg) mg of estradiol benzoate via an i.m, injection on d -9 (d 0 = initiation of the breeding season). All cows recei ved an intravaginal progesterone-releasing insert (IPI; CIDR-B) on d -9. On d -2, the IPI was withdrawn and all cows were administered 500 mu g of clo prostenol sodium. Beginning on d 0, cows were bred by AI upon detection of estrus. Estrus was observed in similar proportions of cows in each treatmen t during the first 6 d of AI (90% across treatments), but the interval to e strus was shorter (P < .05) in 1mg (1.26 +/- .18 d) than in 2mg (1.77 +/- . 18 d). Conception and pregnancy rates did not vary among treatments; howeve r, cows in estrus on d 0 tended to be less fertile (P = .11) than those in estrus on d 1. In Exp. 2, 408 cyclic cows from three herds were assigned to receive either no synchrony treatment (Control, n = 214) or the treatments described in Exp. 1 (1mg, n = 100; 2mg, n = 94). Anestrous cows from all h erds received an IPI from d -9 to -2 (n = 143; Anestrus). All cows in the 1 mg, 2mg, and Anestrus groups, with the exception of those detected in estru s between d -1 and 0, also received 1 mg of estradiol benzoate on d 0. Grea ter than 90% of cows that received an IPI were in estrus between d -1 and 3 , and 92.1% of cows in the Control group were in estrus by d 21. Conception rate to first service in 2mg (61.7%) was similar to Control (57.0%), tende d to be higher (P = .06) than 1mg (49.0%), and was greater (P < .05) than A nestrus (39.9%). The mean day of conception was earlier (P < .05) in the 2m g (d 13.1 +/- 2.0) than the Control (d 23.2 +/- 1.6) and Anestrus (d 22.4 /- 1.9) groups. Conception occurred earlier in 1mg (d 17.4 +/- 2.1) than in Control. The proportion of cows that were pregnant at the end of the breed ing season tended (P = .09) to be greater in the 2mg and Anestrus groups. T his regimen of estrus synchronization improved reproductive competence in c yclic cows and resulted in similar reproductive performance in anestrous co ws and untreated cyclic cows inseminated at a spontaneous estrus.